The present invention generally relates to an internal combustion engine, and more particularly, to a suction arrangement of a V-type internal combustion engine provided with an auxiliary unit, especially, a mechanical supercharger or the like in a space defined between a pair of upwardly diverging left and right side cylinder banks.
Conventionally, as disclosed, for example, in Japanese Utility Model Laid-Open Publication Jikkaisho No. 61-5330, there has been proposed an arrangement in which a mechanical supercharger is disposed between upwardly diverging left and right side cylinder banks of a V-type internal combustion engine for achieving compactness of said engine. Normally, respective cylinders of a V-type internal combustion engine of this kind are a cross-flow type in which exhaust ports are provided outside the cylinder banks, and intake ports are provided at the inner side of the cylinder banks. As also disclosed in the above publication, it is usual intake passages for the left and right side cylinder banks to be curved generally in a horizontal direction and extend to the inner side of the cylinder banks so as to be connected to a delivery port of the mechanical type supercharger. In the above case, however, the layout of the intake passage, manifolds, or inter-cooler, etc., are considerably restricted by the provision of the supercharger in the space between the left and right side cylinder banks, with a consequently large degree of curvature of the intake passage, thus undesirably contributing to large suction resistance.
Incidentally, instead of designing the left and right side intake passages to curve in a horizontal direction so as to be brought under the supercharger as described above, there may be conceived an arrangement in which, by providing intake ports, intake passages of respective cylinder banks are directed in a vertical direction at opposite sides of the supercharger for communicating with said supercharger through manifold pipes at the upper portion of the intake passages. In the above arrangement, comparatively less suction resistance may be expected since the curvature of the intake passages can be relatively small. However, when the intake passages are provided at the opposite sides of the supercharger in the vertical direction, it becomes difficult to properly dispose fuel injectors, with respect to position and orientation, in the vicinity of the intake ports. When the fuel injectors are not provided in the proper position and orientation, a problem arises in that combustion efficiency is deteriorated due to the adhesion of fuel components onto cylinder wall surfaces.